1. Field of the Invention
This invention relates to electrophotographic photosensitive materials used in electrophotographic processes. More particularly, it relates to electrophotographic photosensitive materials in which a photoconductive layer contains a quinocyanine pigment having a particular molecular structure.
2. Description of the Prior Art
As electrophotographic photosensitive materials, inorganic photosensitive materials such as amorphous selenium, selenium alloys, cadmium sulfide and zinc oxide and organic photosensitive materials which include, typically, polyvinylcarbazole and derivatives thereof, are widely known at present.
Amorphous selenium and selenium alloys have very excellent characteristics as electrophotographic photosensitive materials and, therefore, they have been put to practical use, as is well known. They, however, have disadvantages in that their preparation requires complicated processes for deposition and, further, the deposited film formed is not flexible. Zinc oxide is used in the form of photosensitive materials of the dispersion type in which it is dispersed in a resin. Such photosensitive materials have a defect in mechanical strength, so that they are not suitable for repeated operation as they are.
Polyvinylcarbazole which is widely known as an organic photoconductive material has excellent transparency, film-forming properties, flexibility, etc., but itself exhibits no sensitivity in the visible region. Since polyvinylcarbazole, per se, cannot, therefore, be put to practical use, various sensitizing methods have been devised. However, spectral sensitization of polyvinylcarbazole with a sensitizing dye cannot provide sufficient electric characteristics for electrophotographic photosensitive materials, although the spectral sensitivity region is extended into the visible region, and is disadvantageous in that light fatigue is marked. Further, chemical sensitization with an electron-accepting compound can provide satisfactory photographic photosensitive materials from the standpoint of sensitivity, and some such photosensitive materials have been put to practical use, but problems still remain with respect to mechanical strength, life, etc.
Organic photosensitve materials of the dispersion type have been actively studied, and many reports have been made thereon. However, photosensitive materials having excellent electrical characteristics and satisfactory sensitivity as an electrophotographic photosensitive material have still not yet been obtained.
At the present time, it is reported that phthalocyanine exhibits excellent electrophotographic characteristics when used as a photosensitive material of the dispersion type, but the spectral sensitivity of phthalocyanine lies rather toward longer wavelengths and, therefore, it has the defect of poor red-reproducibility.